1. Field of the Invention
This invention relates to an isotropic liquid fabric softening composition and more particularly to a stable isotropic liquid fabric softening composition incorporating a fabric mildewstat.
2. Description of Related Art
Fabric softening compositions, in liquid or particulate form, are well known in the art and have been used in home and commercial laundering of fabrics to impart freshness and softness thereto. Typically, liquid compositions are rinse-added and contain, as an active component, a substantially water-insoluble quaternary ammonium compound, amine, or amine salt. An important consideration in formulating a fabric softening composition is that of ensuring the composition is adequately deposited onto the fabric. Adequate and uniform deposition of the composition is hampered by the varying solubilities and hydrophobicities of the materials comprising the fabric softening composition. Such materials are normally present as oil-in-water suspensions or dispersions, usually with a low content of active. Often such suspension or dispersions are not phase-stable, causing the actives to separate out. Accordingly, efforts have been made to develop phase-stable fabric softening compositions. Particularly advantageous are isotropic compositions. United Kingdom Pat. No. 2,007,734 issued to Sherman et al. describes a liquid non-aqueous fabric softener concentrate comprising a quaternary ammonium salt, an oil or a C.sub.8-24 fatty alcohol, and optionally a nonionic or cationic surfactant. MacGilp et al., U.S. Pat. No. 4,454,049 describes an isotropic fabric softening concentrate comprising an imidazolinium fabric softener, an organic solvent and an esterified polyol.
The use of 3-isothiazolones in aqueous compositions is shown, generally, by Lewis et al., U.S. Pat. Nos. 4,015,431 and 3,523,121, which describe various 3-isothiazolones having biocidic activity at concentrations of about 0.1 to 10,000 ppm. U.S. Pat. Nos. 4,252,694 and 3,761,488, also issued to Lewis both disclose 3-isothiazolones as mildewcides and specifically the 2-n-octyl derivatives as paint (up to 0.25%), water (up to 0.1%), and laundry solution (up to 0.1%) biocides. Lewis '694 also shows the n-octyl derivatives at solution levels up to about 1% as mildewstats for paper and leather. None of the Lewis references, however, teach or suggest the use of 3-isothiazolones in an organic fabric softener matrix. Hinton, U.S. Pat. No. 3,065,123 discloses a process for the control of microorganisms in water by the addition of 1,2-benzisothiazolones. Hennemann et al., U.S. Pat. No. 4,417,895 discloses a process for the antimicrobial treatment of textiles using an azole compound. The process requires washing the textiles with a composition containing an alkyl polyglycol ether, and a quaternary ammonium salt, as well as water or organic solvents, and the azole compound may be included in the composition or separately added. Various adjuncts have been added to fabric softening compositions of the art, including antimicrobial agents. Nuesslein et al., U.S. Pat. No. 4,629,574 describes an aqueous fabric softener including quaternary ammonium or imidazolinium fabric softeners, water-miscible and water-imiscible solvents, water and an acid to adjust the pH to below 6, and may include an (unspecified antimicrobial agent. U.S. Pat. No. 4,424,134 issued to Sissin et al. describes a liquid fabric softening composition including about 0.1 to 20 ppm of 2-chloro-5-methyl-4-isothiazolin-3-one as a composition preservative. Sissin et al. is directed to improving the stability of the 3-isothiazolones in the presence of amines, and utilizes a pH of below about 6 to maintain the efficacy thereof. Fabric mildewcides incorporating about 1-7 ppm of 2-methyl-5-chloro, and 2-methyl 3-isothiazolones are described in Japanese Patent Application 58 216 05 to Mochizuki et al. These 3-isothiazolones are identified as being useful due to a high solubility in water, and a high volatility. U.S. Pat. Nos. 4,499,071 and 4,454,146 both issued to Borovian disclose fabric softening compositions including 0.2 to 1% of 5-chloro-2-methyl- and 2-methyl-3-isothiazolones as composition preservatives. European Patent Application No. 0 150 531 to Witjens describes a clay-containing fabric softening composition and mentions that 2-methyl-4-isothiazolin-3-one and its chloro derivatives can be included at levels of 0.001-.3% as a composition preservative.
The art has been limited to teaching the use of low levels (less than about 20 ppm (0.002%) in the formulation) of the 2-methyl and 5-methyl 3-isothiazolones and their chloro derivatives in aqueous solutions as solution preservatives for laundry compositions. The art is deficient in teaching the use of relatively high levels of any 3-isothiazolones in an isotropic composition, or as a laundry mildewstat having residual mildewstatic effects on fabric treated therewith. Further, it is generally accepted that the 3-isothiazolones are unstable in the presence of primary or secondary amines, which are usually present in fabric softeners.
It is accordingly an object of the present invention to provide an isotropic fabric softening composition which allows delivery of comparatively high effective levels of a fabric mildewstat.
It is another object of the present invention to provide a fabric softening composition with highly substantive fabric softening and antimicrobial materials.
It is a further object of the present invention to provide a fabric softening composition which has a residual mildewstatic effect on fabrics treated therewith.
It is a further object of the present invention to provide a stable isotropic fabric softening composition having a mildewstat incorporated therein.
Briefly, a preferred embodiment of the present invention comprises an isotropic fabric softening composition having the essential components of:
a cationic fabric softener, PA1 an organic solvent matrix; and PA1 a 3-isothiazolone mildewstat active.
The preferred fabric softener is a quaternary ammonium or imidazolinium cationic type having an iodine value of about 20 to 70 (as g of iodine/100 g of unsaturated material) and a melting point below about 25.degree. C. Preferred organic solvents include C.sub.1-4 alkanols, C.sub.2-6 alkylene diols, polyols containing ethers, and mixtures thereof. The 3-isothiazolones are preferably drawn from the class of 2-n-alkyl-4-isothiazolin-3-ones, with the most preferable alkyl groups being in the six to twelve carbon range. It has been surprisingly found that when the isothiazolone is present in the isotropic fabric softening composition at significantly higher levels than found in the art, a residual mildewstatic effect exists to prevent the growth of microorganisms on fabrics treated with the composition. This mildewstatic effect effectively controls malodors on wet fabrics for up to about 168 hours, and continues to exert a long term, residual mildewstatic effect on dried fabrics. As used herein, the term "mildew" refers to any organisms or group of organisms having the tendency to produce malodors on fabrics. Stasis means the inhibition of growth of such organisms, but does not exclude the actual killing thereof.
The composition is added or released during the rinse cycle of the laundering process, and in addition to imparting a soft feel to fabrics, provides immediate high level antimicrobial activity, and continues to impart a residual mildewstatic activity to the fabrics even after drying thereof.
It is therefore an advantage of the present invention that the composition provides immediate, as well as residual, mildewstatic activity.
It is a further advantage of the present invention that a stable, isotropic composition, allowing delivery of relatively high levels of the 3-isothiazolone active, is achieved.
It is another advantage of the present invention that the composition provides a high effective-delivered amount of 3-isothiazolone active to the fabrics.
It is another advantage of the present invention that the composition remains phase-stable for an extended period.
These and other objects and advantages of the present invention will no doubt become apparent to those skilled in the art after reviewing the following Detailed Description of the Preferred Embodiment.